* fbt: optional shallow submodule checkout
* fbt: more git threads by default
* fbt: git condition fix
* fbt: renamed FBT_SHALLOW to FBT_GIT_SUBMODULE_SHALLOW
* github: enabled FBT_GIT_SUBMODULE_SHALLOW in flows
* fbt: always compile icons' .c, even if user does not specify a proper source glob; changed glob to require files at user-specified paths to exist
* fbt: fail build for missing imports in .faps
* fbt: moved STRICT_FAP_IMPORT_CHECK to commandline options; enabled by default
* ufbt: enabled STRICT_FAP_IMPORT_CHECK
Co-authored-by: あく <alleteam@gmail.com>
